Spectroscopic characterization of Megavoltage-Photon Spectra

High-energy, high fluence rate photon sources are used in therapeutic radiation oncology for the treatment of a variety of disease sites. Common dosimetry methods for characterizing these sources use energy-integrating devices such as ionization chambers; however, the most descriptive characterization of these sources are performed with pulse-mode detectors, which preserve the energy-specific information in the source output. This work uses spectroscopic methods to characterize two therapeutic-level megavoltage photon sources, a cobalt-60 teletherapy source and a 6 MV linear accelerator source. The spectra are determined using a Compton scattering measurement technique and Monte Carlo simulations with the MCNP5 transport code. The results of these studies demonstrate the effect that variable source characteristics have on both spectra and dosimetry.